SUBPHYLUM i: CNIDARIA 



113 



shown in Fig. 76 and in section in Fig. 77. From the main 

 digestive cavity a series of radial canals, some branched, run out 



Fig. 76. — A small specimen of the common jelly-tish, Aurelia aurita, natural size. 



Note the horseshoe-shaped gonads, showing through the transparent tissues ; the radial canals, alternately 

 branched and unbranched ; the little sense tentacles in notches each opposite the middle branch of a 

 canal ; the marginal tentacles ; and the arms of the manubrium, each folded and fringed. 



Water circulates from the stomach by the unbranched (adradial) canals to the circular canal, and 

 back by the branched (per- and inter-radial) canals. 



to a circular canal running round the edge of the disc. Through 

 these a circulation of sea water is kept up by ciHa, the stream 



ex.H, 



cau.r' 



sien. 



Fig. 77. — A diagram of a vertical section through one of the large jelly-fishes, 

 such as Aurelia. The section is divided by a dotted line into two halves, m 

 one of which it is supposed to pass through a radial canal, and m the other 

 through the endoderm lamella. 



canx. Circular canal ; can.r., radial canal ; en.L, endoderm lamella ; ex.u., exumbrella ectoderm ; g.. gonad ; 

 g./., gastral hlament ; hd., hood covering sense tentacle; ;., jelly or mesogoea ; m6. manubnum ; 

 CBS., oesophagus ; s.g.p., subgenital pit ; s.ten., sense tentacle ; st., stomach ; ten., tentacle. 



going out by the eight unbranched canals and returning by the 

 alternating branched ones. Partially digested particles of food 

 are carried in the stream, and are ingested by any endodermal 



